There are plenty of apps that can stream movies and TV shows to your tablet or smartphone -- Amazon Instant Video, Crackle, HBO Go, Hulu Plus, Netflix... shall I go on? -- but very few that let you download content for offline viewing.

That's kind of a bummer, because it means if you want to watch something on, say, an airplane, you have little choice but to buy from iTunes or rip from DVDs.

If you're a Comcast subscriber, now you have another option. The newly updated Comcast Xfinity TV Player app (Android|iOS) now offers the enviable ability to download movies and TV shows from four networks: Encore, MoviePlex, Showtime, and Starz.

That's kind of a big deal. And it works, too, at least on the iPad and Samsung Galaxy S III that I used for testing. As long as you already have those channels as part of your Comcast subscription, you'll see a Download button alongside the Play button that appears when you browse the app's on-demand content.

The app gives you a choice between "medium" and "highest" quality for your downloads, the latter potentially chewing up your available storage in a hurry. To get "21 Jump Street" at highest quality, for example, you'll need 2.4GB of free space. However, the medium-quality version consumes just 478MB -- and to my eyes looked decent enough, especially on smaller screens.

Obviously it would be great if this download option extended to all Comcast's offerings, especially HBO, but certainly there's some good viewing to be found here. Showtime, of course, is home to "Homeland," "Dexter," "Episodes," and "Nurse Jackie," among other critically acclaimed series. (Movie selection: meh.) And on Starz I found not only "Boss," "Party Down," and "Torchwood: Miracle Day," but also the aforementioned "21 Jump Street" and "Moneyball."

So, yeah, if you're a Comcast pay-channel subscriber, now you can pack your phone or tablet with good stuff for your next flight. Here's hoping some of those other apps I mentioned (cough, HBO Go, cough) will follow Comcast's awesome lead.